Iran has expanded its potential capacity to refine uranium in an underground site by doubling its centrifuges from 1,064 to 2,140, an International Atomic Energy Agency (IAEA) report said on Thursday.

According to the latest quarterly report on Iran's disputed nuclear program, Iran continues its uranium enrichment and hides the 2,140 centrifuges in Fordow facility, of which 696 were operating.

The report also said the nuclear facilities were buried deep inside a mountain for better protection against military strikes.

According to the report, Tehran has increased its high-level uranium 44kg since May, to a total of 189 kg at present.

The UN nuclear watchdog urged Iran to immediately open Parchin Military Base to UN inspectors to clarify its nuclear program.

The West worries about Tehran's nuclear ambitions, accusing Iran of developing nuclear weapons in cover of peaceful purpose, which has been denied by Iran.